|Publication number||US7959775 B2|
|Application number||US 11/536,806|
|Publication date||Jun 14, 2011|
|Filing date||Sep 29, 2006|
|Priority date||Sep 29, 2006|
|Also published as||US20080083615|
|Publication number||11536806, 536806, US 7959775 B2, US 7959775B2, US-B2-7959775, US7959775 B2, US7959775B2|
|Inventors||Mirko Vukovic, Ronald Nasman|
|Original Assignee||Tokyo Electron Limited|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Classifications (8), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to vacuum processing systems, particularly plasma processing systems that couple RF energy through a dielectric window to excite a plasma within a vacuum processing chamber.
In many vacuum processing systems, for example those used in the semiconductor manufacturing industry, a dielectric or ceramic window is employed in the wall of a vacuum chamber to provide transparency for the coupling of RF energy through the wall and into the chamber to support a plasma within the chamber. In many deposition systems, including ionized physical vapor deposition (iPVD) systems, and in some etch systems, metal vapor that is present in the chamber has a tendency to form an electrically conductive film on the inside of the window. The film allows electrical currents to be induced that heat the window, which in many cases causes the window to fail. Catastrophic failure of the dielectric window in some cases can result in loss of an expensive substrate, and in all cases results in costly maintenance and non-productive down-time of the processing equipment.
Better analysis of the causes of such failures and the better prevention of such failures are needed.
An objective of the present invention is to extend the life of a ceramic or dielectric window that tends to collect electrically-conductive film deposits in a plasma processing machine.
A more particular objective of the present invention is to reduce the heating effects on a dielectric window caused by the presence of metal film deposits of the window.
According to principles of the present invention, metal film thickness or metal film continuity are controlled by features on or adjacent the chamber side of a dielectric window in a plasma processing chamber.
According to certain embodiments of the invention, window heating is reduced by breaking the metal film current path by providing features at the window surface, and alternatively or in addition, by reducing the film thickness by increasing the window surface area.
The illustrated embodiments of the invention provide alternative methods of reducing the window heating, including forming overhang structure across the metal film current path on the window surface or reducing the film thickness by texturing the film surface to increase surface area.
These and other objects and advantages of the present invention will be more readily apparent from the following detailed description of illustrated embodiments of the invention.
One type of plasma processing apparatus that uses a dielectric or ceramic window in the wall of a vacuum processing chamber is an iPVD apparatus, an example of which is described in U.S. Pat. No. 6,719,886. The dielectric window in this apparatus provides RF transparency in the chamber wall to facilitate the generation of an inductively coupled plasma (ICP) in the chamber from a coil or other antenna outside of the chamber. Etching and deposition processes performed in the chamber can result in the formation of electrically-conductive, metal film formation on the inside of the window. Deposition baffles can be provided inside the window to retard and interrupt the film formation to prevent the film from reducing the coupling of RF power through the window. Some film eventually forms on the window, and supports induced current that can lead to the heating of the window through RF power being deposited into the window. The heating of the window can lead to a structural failure of the window as thermal stresses develop in the ceramic material of which the window is made.
Applicant has concluded that there are two primary RF power deposition mechanisms due to metal coating of the ceramic window in the iPVD module that produce heating of the window. The mechanisms include dielectric dissipation and resistive heating of the metal film. The currents in the metal film can be induced by capacitive coupling due to the differential voltage on the RF coil that is outside of the window and by induction from the fluctuating magnetic field from current in the coil. The dominant heating mechanism is believed to be dielectric dissipation, that is, heating by motion imparted to atoms in the dielectric window material as a result of currents induced in the film. About 20 watts of heating is attributed to this mechanism. Resistive heating as a result of current induced in the film or the dielectric material is believed to be negligible.
The ceramic vacuum window in the iPVD module is subject to thermal stresses and breakage when the deposited metal layer becomes continuous. Heat dissipation of about 100 watts in the central window region is sufficient to cause window breakage, which can be attributed to hoop (tensional) stresses along the window periphery due to the window expansion in the center.
Capacitive coupling between the coil and the metal film is one mechanism, by which a window is heated.
When the metal film 15 is deposited on the window 14, a circuit comprising of capacitive coupling between the coil ends and the metal film is formed. This circuit is shown on
From observation, the thickness of interest of the metal film 15 is in the range of from 1 to 5 microns, or typically around 2 microns. This thickness, where the film 15 is of copper, is much smaller than the skin depth, which is about 18 microns. Peak-to-peaks voltage on the coil can be about 9 kV. For an alumina window, calculations and modeling will show that power dissipation in the dielectric can be about 13 watts, with resistive power loss in the film 15 being about 4.5 watts for an exemplary configuration.
However, when the film is very thin such that when the film resistance is in the order of the capacitive impedance of the circuit, maximum power dissipation in the order of 100 watts could theoretically occur. But such high power loss is somewhat avoided by the use of a bridged baffle of the type described in U.S. Pat. No. 6,946,054. where the bridges prevent the circuit from closing while the deposits under the slots 18 of the baffle 16 are thin. That is, once a film builds up beneath the bridges, the rest of the coating is sufficiently thick to avoid large resistive power losses.
Induced current flows also result in power dissipation. If the film thickness were greater than the skin depth, current could loop around both sides of the film and result in power dissipation in the order of 1,000 watts. For thin films, current is much lower, and the dissipated power is lower, but nonetheless varies in proportion to the thickness cubed. So reduction of film thickness by 50% reduces heat load by about 87.5%. Inductive heating power can be estimated to be 1 watt for a 2 micron film, about 3.5 watts for a 5 micron film, and about 30 watts for a 10 micron film.
Accordingly, resistive heating of the metal film due to inductive heating, and due to capacitive coupling can become important for very thin and very thick films (much less than or much greater than one micron), dielectric dissipation is the dominant heating mechanism that accounts for window breakage.
Prevention of dielectric heating has been approached by attempts to reduce or eliminate metal deposition on the window through baffle design. Design of the window and source structure to eliminate the stress concentrations in the window can help the window withstand dielectric heating and improve the window lifetime. Use a higher thermal conductivity material for the window, for example, using aluminum nitride instead of aluminum oxide to provide a much higher thermal conductivity and smaller thermal expansion coefficient are also helpful in lessening window breakage. Furthermore, use of a structurally floating element that will become coated and heated instead of the window will also extend window life. Since such can element would be structurally floating, it would be less subject mechanical stresses.
Dissipation losses and other losses due to currents in the metal film can be reduced by breaking the current path in the film or by reducing the film thickness. Breaking the current path can be achieved by splitting the metal film. The pattern of the film 15 can be controlled to that illustrated in
The providing of a break 30 in the film 15 can be achieved by providing a self-shadowing feature on the chamber side of the window 14. One example of a self-shadowing feature is the raised feature 40 shown in an exaggerated form in
Another example of a self-shadowing feature is shown on
In addition or in the alternative to the above, it is proposed to reduce the heating power in the window 14 by decreasing the thickness of the film 15. The film can be decreased by increasing the surface area on the chamber side of the window. The total heating power would then be proportional to inverse area squared. Increasing the surface area of the window 14 on the chamber side can be achieved by creating a series of grooves 60 in the surface window 14, on the side facing the chamber. An example of this is the window 14 in
Another way of increasing the surface area of the window is to use an array pyramid-like features 70 as shown on
Although only certain exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US5763851 *||Jul 3, 1996||Jun 9, 1998||Applied Materials, Inc.||Slotted RF coil shield for plasma deposition system|
|US6132566 *||Jul 30, 1998||Oct 17, 2000||Applied Materials, Inc.||Apparatus and method for sputtering ionized material in a plasma|
|US6623595 *||Mar 27, 2000||Sep 23, 2003||Applied Materials, Inc.||Wavy and roughened dome in plasma processing reactor|
|US6719886 *||Jun 29, 2001||Apr 13, 2004||Tokyo Electron Limited||Method and apparatus for ionized physical vapor deposition|
|US6946054||Feb 22, 2002||Sep 20, 2005||Tokyo Electron Limited||Modified transfer function deposition baffles and high density plasma ignition therewith in semiconductor processing|
|US20030159782 *||Feb 22, 2002||Aug 28, 2003||Tokyo Electron Limited||Modified transfer function deposition baffles and high density plasma ignition therewith in semiconductor processing|
|US20050011453 *||Aug 18, 2004||Jan 20, 2005||Tomohiro Okumura||Plasma processing method and apparatus|
|US20060137821 *||Dec 28, 2004||Jun 29, 2006||Lam Research Coporation||Window protector for sputter etching of metal layers|
|U.S. Classification||204/298.02, 204/298.11, 204/298.18|
|Cooperative Classification||H01J37/32522, H01J37/321|
|European Classification||H01J37/32M8D, H01J37/32O4H|
|Oct 16, 2006||AS||Assignment|
Owner name: TOKYO ELECTRON LIMITED, JAPAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:VUKOVIC, MIRKO;NASMAN, RONALD;REEL/FRAME:018394/0353
Effective date: 20061006
|Nov 13, 2014||FPAY||Fee payment|
Year of fee payment: 4